Heating apparatus for plastic extruders

ABSTRACT

A heating unit comprising a chamber in which are located at least two electrodes. The electrodes each comprising a first portion matching and secured to the interior wall of the chamber and a second portion extending radially inward toward the central axis.

United States Patent [19'] Maurer et a].

HEATING APPARATUS FOR PLASTIC EXTRUDERS Inventors: Karel -Maurer,l-lradec Kralove; I

Ladislav Benda, Plotiste Nad Labem, both of Czechoslovakia Assignee:Tesla, Narodni podnik, Praha,

Czechoslovakia Filed: Nov. 18, 1971 Appl. No.: 199,861

US. Cl 13/23, 219/291, 425/174.6 Int. Cl. F27d 11/04 Field of Search13/23; 425/174.6;

[ Dec. 18, 1973 [56] References Cited UNITED STATES PATENTS 3,335,4608/l967 Radl ..425/174.6 2,8l7,695 l2/l957 Hartwig l3/23X PrimaryExaminerRoy N. Envall, Jr. Attorney-Richard Low et al.

[5 7] ABSTRACT A heating unit comprising a chamber in which are locatedat least two electrodes. The electrodes each comprising a first portionmatching and secured to the interior wall of the chamber and a secondportion extending radially inward toward the central axis.

13 Claims, 8 Drawing Figures HEATING APPARATUS FOR PLASTIC EXTRUDERS Thepresent invention relates to apparatus for extruding plastic masses andin particular to apparatus for extruding clay or ceramic objects.

One of the main functions of apparatus of this type is to provide aneven and uniform heating of the plastic material during its extrusion.In general this is performed by the distribution and shape of one ormore electrodes within a heater unit. Conventionally the heater body ishollow and cylindrical or conical in shape and is located, either as anintegral or separable member, between the worm or press chamber and theforming or shaping die out of which the plastic mass is extruded. Theelectrodes are connected to conventional sources of current andtransform the hollow body into a heating chamber for the plastic.

In the prior devices the electrodes have been connected to a source ofuniphase A.C. current, with one of the electrodes being in the form of aring located on the inside surface of the hollow body and the otherelectrode in the form of a conductive mandrel located along the axis ofthe heating chamber. In extruders for small size objects the unevennessin heating the plastic mass is balanced and the heat uniformlydistributed by the intensive mixing of the material as it is beingforcefully extruded through the narrow orifice of the nozzle, the crosssection of which is between 100 and 1000 times smaller than the crosssection of the heating chamber. This situation is, however, differentfor the extrusion of pieces of large shapes and sizes, as for instancebricks or high voltage insulators, since the unevennesss of the heatingprocess within the heating chamber can not be balanced by the mixing ofthe mass in the die. In this latter instance the die orifice is at mostonly ten times smaller than the cross section of the heating chamber. Inthese larger extruders it has been necessary to use a three phasecurrent source for the electrodes. Therefore the devices must containthree or a multiple of three electrodes. Notwithstanding the use of anincreased current source the distribution of individual electrodes aboutthe circumference of the heating space has not resulted in an evendistribution of the heat, particularly along its central axis. Convexelectrodes, that is, curved to conform with the shape of the body, havebeen tried, resulting in a more even distribution of electric currentfield, but they do not achieve a more even distribution of the heatingtemperature. The heatalong the central axis is higher than the outside.The convex electrodes are furthermore not convenient because they reducethe transflux cross section and retard the movement of the plastic massaround the electrodes, although the movement of the mass along thecentral axis is faster.

It is an object of the lpresent invention to provide extruding apparatusof the type described which creates a more even and uniform distributionof heat within the entire cross section of the plastic mass.

It is another object of the present invention to provide extrudingapparatus of the type described in which large pieces and objects maybeformed.

It is yet another object of the present invention to provide extrudingapparatus in which uniform mixing of the heat mass may be obtained withthe use of large I die orifices. i

These objects, others and numerous advantages will be apparent from thefollowing disclosure of the preferred embodiment of the presentinvention.

SUMMARY OF THE INVENTION According to the present invention apparatusfor heating the plastic mass in extrusion devices is provided comprisinga chamber having a longitudinal axis in which at least two electrodesare located. Each electrode comprises a first portion securedinsulatingly to the inner wall of the body and a second portionextending radially toward the central axis. The two portions are atleast conductively connected to form a unitary electrode body and are ofsuch size and configuration to evenly distribute the heat withoutreduction of the transilux cross section of the body.

Preferably the electrodes are connected to a three phase current sourcein wye or delta networks. The

inner portion may be provided with a curved or convex configurationwhile the outer portion is curved to match the arc or configuration ofthe body. A mandrel or shaft may also be located along the central axisand may be connected into the current source network.

Full details of the present invention will be seen in the attacheddrawing and in the following description.

BRIEF DESCRIPTION OF DRAWING In the drawing:

FIG. I is an axial cross section of a heating apparatus according to thepresent invention,

FIG. 2 is transverse sectional view of the apparatus of FIG. 1,

FIGS. 3 and 4 are views similar to FIGS. 1 and 2 respectively showing asecond embodiment of the present invention,

FIGS. 5 and 6 are views similar to FIGS. 1 and 2 respectively, showing athird embodiment, and

FIGS. 7 and 8 are views similar to FIGS. 1 and 2 showing yet a fourthembodiment.

Before turning to the description of the present invention it will beunderstood that the drawings show only the heating unit and chamber andassociated apparatus. The remaining extruder apparatus such as the worm,screw or other compression means, the die, the sources of current,control means, etc., are omitted from the drawings for the sake ofbrevity. These nonillustrated mechanisms are well known and do notrequire description or showing here for the understanding of the presentinvention.

DESCRIPTION OF INVENTION In all four of the illustrated embodiments aplurality of electrodes 1 comprising an external portion 2 and aninterior portion 3 are located within the hollow space formed by a body4 having an axial central axis 0. The body 4 may be cylindrical orconical although as seen, it is generally cylindrical and has a leadingconical tapered discharge end portion in which an orifice 8 is formedfor discharge of material. The body 4 is adapted to be secured betweenthe non-illustrated worm or compression means and the shape forming dieand its interior defines a heating space or chamber 5 wherein theplastic material acted upon by the electrodes and constituting a portionof the electrical resistance circuit is-elevated in temperature toattain its proper extrusion plasticity. The interior surface of the bodyis'preferably coated with-electrically insulating material-or at leastsuch material is interposed between the internal portion 2 of theelectrode and the surface of the body 4.

The external portion 2 of the electrode is insulatingly secured to theinternal surface of body 4 and the internal portion 3 extends radiallyinward toward the central axis. The two portions 2 and 3 are bothmechanically and electrically connected, preferably being integrallyand/or unitarily formed of suitable electrode conductive material. Theexternal part 2 is matched to the shape of that portion of the body 4 atwhich it is located. That is, it is transversely curved to the arc ofthe body and extends over a substantial portion thereof rather thanhaving merely a point or line configuration and attachment. For example,when placed in a cylindrical body the external portion 2 comprises acylindrical segment and when placed in a conical body it comprises aconically curved section. This provides a generally even distribution ofpower along the crosssectional periphery of the body and the greatesttransflux cross-sectional movement can be achieved. The surface of theinternal portion 3 is for optimum results kept at least equivalent to afifth of the surface of the external portion 2 and extends radially intothe body 4 to a depth of at least a third of the radius of the bodymeasured from its interior surface. This provides for an even anduniform distribution of heat toward the central axis and balances theheat provided at the crosssectional periphery.

The individual embodiments differ from each other as follows:

In the arrangement seen in FIGS. 1 and 2 the internal portion 3 forms aradial rib which may have a terminal head at its inner end. This rib isintegrally connected to the external portion 2. Preferably, the twoportions are formed unitarily from the same piece of material althoughthey may be separately formed and then mechanically and electricallyconnected. The electrodes are arranged triangularly in a delta networkto a source of three phase current.

In the arrangement according to FIGS. 3 and 4 the internal portion 3 isin the form of an elongated longitudinally directed plate or strip, thelongitudinal direction extending parallel to the axis of the body 4. Theprofile of the internal portion 3 is curved in cross section convexedlywith respect to the central axis and is connected to the externalportion 2 by a radial strut or supporting piece 6 of small cross sectionperpendicular to its longitudinal axis. This construction creates only aminimum reduction in the transflux cross section of the heating chamber.It is noted that the curve of the inner portion 3 flares away from thecenter of the heating chamber being opposite in general form to the arcof the body. Rather than a convex curve the inner portion may be bentalong its center to form an inverted V- or U-shape. As in the precedingembodiment the portions 2 and 3 and the strut 6 may be formed from onepiece of material or they may be separately made. The electrodes arealso connected in a triangular delta network to the current source.

In the arrangement of FIGS. 5 and 6 the electrodes 1 may have the sameshape as those in either of FIGS. 1 and 2 or FIGS. 3 and 4, but here aconductive mandrel 7, either as a solid rod or hollow tubular shaft, islocated cantilevered along the central axis. The mandrel 7 is held by aplurality of holding brackets 9 radially extending to the interiorsurface of the body 4. The electrodes 1 maybe connected in a wyeor'spidernetwork to a source of three phase current while the mandrel 7is connected to the node or common point of the circuit arrangement. Inthis manner the electrodes 1 and the mandrel 7 both act as heatingsource. It will be noted that the mandrel 7 extends from within thenonillustrated compression chamber partially through the heating spaceterminating in a conical or bullet nose end short of the discharge coneand opening 8.

The arrangement according to FIGS. 7 and 8 is similar to that of FIGS. 5and 6 except that the conductive mandrel 7 extends the full length ofthe chamber 5 through the discharge cone and into the opening 8, butdoes not necessarily extend from the compression chamber. It ispreferably secured at its rear end to a reinforced bracket 9. Themandrel 7 here may preferably be a hollow tube open at its forward end,or it may be shaped as seen in the preceding FIGS. 5 and 6.

It will be seen that in each embodiment the electrode comprises twoparts. The outer portion, located on the surface of the body, covers asubstantial portion thereof, while the inner portion extends toward thecentral axis. The capacity and effect of the inner portion can beenhanced by convexedly curving the portion away from the central axisthus producing a more even distribution of heat. Both parts aremechanically and electrically connected. Preferably, at least twoelectrodes are used, although when three electrodes 1 are employed, ortheir multiple, connection to a three phase current source in eitherdelta or wye networks is easily possible. The electrodes are uniformlyspaced about the transverse cross section of the body. Thus, almost noreduction in the transflux movement occurs although the heat source(i.e. electrodes) is shifted toward the center of the heating chamber.

The size of the electrodes, particularly in the width dimension, willvary with respect to the size of the body 4 or heating chamber 5. Inaddition it will be beneficial to vary the width of the electrode in anyinstallation in the direction of the longitudinal axis of the body toadjust and accommodate for the changes in electrical resistance of theplastic mass. As the plastic mass moves forward from the compressionchamber to the discharge opening 8 the heat and manipulation within thechamber 5 increases its plasticity thus modifying electrical resistance.As a consequence the electrode at the forward end need not be of thesame size as at the rearmost end. Generally the size will be less as theresistance is less.

It will also be seen that the present invention provides for the uniformand even distribution of heat and the effective plasticizing of thematerial not withstanding the size of the plastic particles or the sizeof the die. The die may be very large but sufficient plasticity will beobtained from working of the material within the heating chamber and bythe heat supplied from the electrodes.

Various other modifications, embodiments and changes can be made and itis intended therefore that the present disclosure be taken asillustrative only and not limiting of the present invention.

What is claimed:

1. In an extruder for clay, ceramic and the like materials, heatingapparatus comprising a heating chamber formed from a hollow body havinga central axis and an insulated interior surface, and at least twoelectrodes located within said body and connected to a source of.current, each of said electrodes comprising an elongated internal andexternal portion extending parallel to the central axis conductivelyconnected with each other to form a unitary member, the external portionbeing insulatingly secured to the interior surface of said body and theinternal portion spaced from said surface and extending radially inwardtoward the central axis of said body.

2. The apparatus according to claim 1', wherein the internal portion ofthe electrode has the form of a rib connected to the external portion ofthe electrode.

3. The apparatus according to claim 1, wherein the internal portion ofthe electrode has the shape of an elongated plate or strip, thelongitudinal direction of the latter being parallel with the axis of thebody and being connected to the external one by means of a radial strut.

4. The apparatus according to claim 1 wherein the cross sectiontransverse to longitudinal direction of the internal portion of theelectrode is curved.

5. The apparatus according to claim 1, wherein the cross sectiontransverse to longitudinal direction of the internal portion of theelectrode is an inverted V-shape.

6. The apparatus according to claim 1, wherein the shape of the externalpart of the electrode is matched to the shape of that part of theinternal surface of the body at which the external part of the electrodeis located.

7. The apparatus according to claim 1, wherein the external part andinternal portion of the electrode are made of one piece.

8. The apparatus according to claim 1, wherein the surface of theinternal portion of the electrode is at least equal to a fifth of thesurface of the external portion of the electrode.

9. The apparatus according to claim 1, wherein the width of theelectrodes in the direction of the central axis is varied in dependenceon the change of the electrical resistance of the plastic mass as aresult of change of temperature in its passage through the heatingchamber.

10. The apparatus according to claim 1, wherein the internal portion ofthe electrode penetrates into the depth of at least one third of theradius of the body, measured from the internal surface.

11. The apparatus according to claim 1, wherein the electrodes areconnected in delta to a three phase current source.

12. The apparatus according to claim 1, wherein the electrodes areconnected in wye to a three phase current source, and a conductivemandrel is located to extend along the central axis of the body, saidmandrel being connected to the node of the three phase current source.

13. The apparatus according to claim 12, wherin the conductive mandrelextends through the body to its ori-

1. In an extruder for clay, ceramic and the like materials, heatingapparatus comprising a heating chamber formed from a hollow body havinga central axis and an insulated interior surface, and at least twoelectrodes located within said body and connected to a source ofcurrent, each of said electrodes comprising an elongated internal andexternal portion extending parallel to the central axis conductivelyconnected with each other to form a unitary member, the external portionbeing insulatingly secured to the interior surface of said body and theinternal portion spaced from said surface and extending radially inwardtoward the central axis of said body.
 2. The apparatus according toclaim 1, wherein the internal portion of the electrode has the form of arib connected to the external portion of the electrode.
 3. The apparatusaccording to claim 1, wherein the internal portion of the electrode hasthe shape of an elongated plate or strip, the longitudinal direction ofthe latter being parallel with the axis of the body and being connectedto the external one by means of a radial strut.
 4. The apparatusaccording to claim 1 wherein the cross section transverse tolongitudinal direction of the internal portion of the electrode iscurved.
 5. The apparatus according to claim 1, wherein the cross sectiontransverse to longitudinal direction of the internal portion of theelectrode is an inverted V-shape.
 6. The apparatus according to claim 1,wherein the shape of the external part of the electrode is matched tothe shape of that part of the internal surface of the body at which theexternal part of the electrode is located.
 7. The apparatus according toclaim 1, wherein the external part and internal portion of the electrodeare made of one piece.
 8. The apparatus according to claim 1, whereinthe surface of the internal portion of the electrode is at least equalto a fifth of the surface of the external portion of the electrode. 9.The apparatus according to claim 1, wherein the width of the electrodesin the direction of the central axis is varied in dependence on thechange of the electrical resistance of the plastic mass as a result ofchange of temperature in its passage through the heating chamber. 10.The apparatus according to claim 1, wherein the internal portion of theelectrode penetrates into the depth of at least one third of the radiusof the body, measured from the internal surface.
 11. The apparatusaccording to claim 1, wherein the electrodes are connected in delta to athree phase current source.
 12. The apparatus according to claim 1,wherein the electrodes are connected in wye to a three phase currentsource, and a conductive mandrel is located to extend along the centralaxis of the body, said mandrel being connected to the node of the threephase current source.
 13. The apparatus according to claim 12, wherinthe conductive mandrel extends through the body to its orifice.